I have looked for ages and cannot seem to find a simple circular Air valve MVpart to use. I work for a HVAC company and we have parts for supply grilles and extract grilles but i have had no luck finding air valves that we use in toilet air Supply and Extract. Can anyone point me in the direction of some, I hope at some point to be able to model some very simple blocks but at the present time I have very little spare time at work to do so. I was hoping that then instead of calculating duct sizes i could use the air valves and the code within MEP to calculate the duct sizes for me.